Little grazer species effect on the vegetation in a rotational grazing system

To maintain and enhance phytodiversity of complex permanent swards, the choice of livestock is still being debated. In this study, vegetation composition, diversity and sward structure of permanent grassland were investigated in response to cattle, sheep or mixed grazing on two sward types differing in composition. The study was conducted in the Solling Uplands in Lower Saxony, Germany, in a triplicate randomized block design. The experimental site belongs to the plant association Lolio-Cynosuretum and is moderately species-rich. One half of the paddocks was treated with herbicides to achieve grassdominated, species-poor swards (2007: 6.9+-1.5 species m-2, means +-sd) in contrast to the diverse controls (10.3+-2.9 species m-2). Paddocks were grazed rotationally in three grazing cycles per year from 2007 to 2011; the vegetation was analyzed from 2007 to 2012. Vegetation composition showed a clear effect of herbicide-treatment, but was not significantly influenced by grazers within or after five years of grazing. With respect to vegetation composition and sward structure, there was no indication of complementary grazing between cattle and sheep in mixed stocking. The effects of grazers in this study were relatively minor and not consistently found. Sward structure, measured as coefficient of variation of sward height, was more heterogeneous in the second grazing cycle 2011 under cattle grazing in contrast to sheep grazing. In addition, the cattle-grazed diverse swards contained more species than the sheepgrazed ones in 2012. These results point toward a slight advantage of cattle grazing for the diversity of European grasslands in common agricultural practice.